The objective of this research program continues to be a comprehensive, systematic, and parametric evaluation of developing auditory perception in an appropriate animal model. By being able to make careful psychoacoustical measures in a developing neonate we hope to greatly extend knowledge about the normal development of auditory perception, and by comparison with other physiological and anatomical research, greatly extend our knowledge about the relationship between structure and function in the developing auditory system. The main section of this proposal continues controlled psychophysical studies of how various thresholds change over the first few postnatal days. Adaptive procedures and signal detection analyses will be used to evaluate both frequency and temporal resolution in neonates. Specifically, these experiments involve tone-on-tone, notched-noise, and band-limited masking functions; gap-detection, frequency-modulation, and amplitude- modulation thresholds; intensity difference limens; and absolute thresholds to a naturalistic stimulus. A secondary section continues experiments that use multidimensional scaling procedures to produce "maps" of how neonates respond to more complex auditory stimuli. In conclusion, these experiments provide a unique and valuable opportunity to carefully document changing auditory perceptions in a developing neonate. In addition to contributing to our understanding of normal hearing this program of research should also help us understand how abnormal development may lead to communicative disorders.